It had hoped to achieve steady state production in mid-to-late 2018 and has now issued full-year guidance of 387,000-407,000 ounces.

The mine produced 111,340 ounces of gold in the June quarter at a grade of 14.9g/t, taking its first half production to more than 187,000oz, within guidance of 150,000-200,000oz.

Pretium is now expecting to deliver 200,000-220,000oz in the second half.

Underground development has been increased from 420m to 700m per month and the quarter also reflected the full integration of the operational grade control programme.

"The successful integration of our grade control programme into our mining process has resulted in increased grade to the mill with production exceeding grade control estimates for the quarter," president and CEO Joseph Ovsenek said.

Pretium declared commercial production at the mine in July 2017 and overcame setbacks in the fourth quarter with an improved March quarter.

It has put all-in sustaining costs for the second half at US$710-$770/oz sold and said it would now place "an increased focus" on operational efficiency to reduce costs.

The company has had recent exploration success at its Valley of the Kings resource and is planning to start a regional, grass roots exploration programme this month.  

Pretium shares, which have ranged between C$7.93-$15.52 over the past year, closed up almost 15% to $12.17, capitalising it at $2.2 billion.